NF-κB is a transcription factor which mediates extracellular signals responsible for induction of genes involved in pro-inflammatory responses (Baltimore et al., (1998) U.S. Pat. No. 5,804,374). NF-κB is anchored in the cytoplasm of most non-stimulated cells by a non-covalent interaction with one of several inhibitory proteins known as IκBs (May & Ghosh, (1997) Semin. Cancer. Biol. 8, 63–73; May & Ghosh, (1998) Immunol. Today 19, 80–88; Ghosh et al., (1998) Annu. Rev. Immunol. 16, 225–260). Cellular stimuli associated with pro-inflammatory responses such as TNFα, activate kinases, which in turn activate NF-κB by phosphorylating IκBs. The kinases that phosphorylate IκBs are called IκB kinases (IKKs).
Phosphorylation targets IκBs for ubiquitination and degradation. The degradation and subsequent dissociation of IκBs from NF-κB reveals the nuclear localization signal on NF-κB, resulting in nuclear translocation of active NF-κB, leading to up-regulation of genes responsive to NF-κB (May & Ghosh, (1997) Semin. Cancer. Biol. 8, 63–73; May & Ghosh, (1998) Immunol. Today 19, 80–88; Ghosh et al., (1998) Annu. Rev. Immunol. 16, 225–260; Siebenlist et al., (1994) Annu. Rev. Cell Biol. 12, 405–455). Phosphorylation of IκBs is therefore an essential step in the regulation of NF-κB mediated pro-inflammatory responses.
The identification and characterization of kinases that phosphorylate IκBs has led to a better understanding of signaling pathways involving NF-κB activation. Several different subtypes of IKK have been identified thus far. IKKα was initially identified as an IκB kinase induced by TNFα stimulation in HeLa cells (DiDonato et al., (1997) Nature 388, 548–554). Another IκB kinase homologous to IKKα was identified, termed IKKβ and determined to be the major IκB kinase induced following TNFα stimulation (Takeda et al., (1999) Science 284, 313–316; Hu et al., (1999) Science 284, 316–320; Li et al., (1999) Science 284, 321–325; Pot et al., (2000) U.S. Pat. No. 6,030,834; Woronicz & Goeddel (1999) U.S. Pat. No. 5,939,302). IKKα and IKKβ have an overall homology of 52% and a 65% homology in the kinase domain (Zandi et al., (1997) Cell 91, 243–252).
IκB protein kinases (IKKs) phosphorylate IκBs at specific serine residues. For example, they specifically phosphorylate serines 32 and 36 of IκBα (Traenckner et al., (1995) EMBO J. 14, 2876–2883; DiDonato et al., (1996) Mol. Cell. Biol. 16, 1295–1304). Phosphorylation of both sites is required to efficiently target IκBα for degradation. Furthermore, activation of IKKα and IKKβ is usually in response to NF-κB activating agents and mutant IKKα and IKKβ, which are catalytically inactive, can be used to block NF-κB stimulation by cytokines such as TNFα and IL-1 (Régnier et al., (1997) Cell 90, 373–383; Delhase et al., (1999) Science 284, 309–313). IκB protein kinases are therefore essential in the regulation of NF-κB activation processes.
IKKα and IKKβ have distinct structural motifs including an amino terminal serine-threonine kinase domain separated from a carboxyl proximal helix-loop-helix (H-L-H) domain by a leucine zipper domain. These structural characteristics are unlike other kinases, and the non-catalytic domains are thought to be involved in protein-protein interactions. Proteins which bind to IKKs may therefore be capable of regulating the activity of NF-κB (Marcu et al., (1999) U.S. Pat. No. 5,972,655) and potentially regulating downstream events such as induction of NF-κB. For instance, NEMO (NF-κB Essential Modulator) is a protein which has been identified to bind to IKKs and facilitate kinase activity (Yamaoke et al., (1998) Cell 93, 1231–1240; Rothwarf et al., (1998) Nature 395, 287–300; Mercurio et al., (1999) Mol. Cell. Biol. 19, 1526–1538; Haraj & Sun, (1999) J. Biol. Chem. 274, 22911–22914; Jin & Jeang, (1999) J. Biomed. Sci. 6, 115–120).
Inflammation is defined as the reaction of vascularized living tissue to injury. As such, inflammation is a fundamental, stereotyped complex of cytologic and chemical reactions of affected blood vessels and adjacent tissues in response to an injury or abnormal stimulation caused by a physical, chemical or biological agent. Inflammation usually leads to the accumulation of fluid and blood cells at the site of injury, and is usually a healing process. However, inflammation sometimes causes harm, usually through a dysfunction of the normal progress of inflammation. Inflammatory diseases are those pertaining to, characterized by, causing, resulting from, or becoming affected by inflammation. Examples of inflammatory diseases or disorders include, without limitation, asthma, lung inflammation, chronic granulomatous diseases such as tuberculosis, leprosy, sarcoidosis, and silicosis, nephritis, amyloidosis, rheumatoid arthritis, ankylosing spondylitis, chronic bronchitis, scleroderma, lupus, polymyositis, appendicitis, inflammatory bowel disease, ulcers, Sjorgen's syndrome, Reiter's syndrome, psoriasis, pelvic inflammatory disease, orbital inflammatory disease, thrombotic disease, and inappropriate allergic responses to environmental stimuli such as poison ivy, pollen, insect stings and certain foods, including atopic dermatitis and contact dermatitis.
Inflammatory diseases present a worldwide problem. Studies of disease burden have re-affirmed that tuberculosis is among the top 10 causes of death in the world. Asthma affects 5% of the adult population and 10–15% of the population of children (Armetti and Nicosia (1999) Boll Chim. Farm. 138(11):599). Asthma is a chronic inflammatory disease that is associated with widespread but variable airflow obstruction.
Sepsis is yet another inflammation disorder and is caused by the presence of various pus-forming and other pathogenic microbes, or their toxins, in the blood or tissues of a subject. Sepsis is characterized by a systemic inflammatory response to bacterial products during infection. The symptoms of sepsis, such as fever, are caused at least in part by the inflammatory response of the body to the infecting agent.
Accordingly, there is still a great need for compounds useful for treating inflammatory disorders.